This application claims the benefit of Korean patent application No. 1997-45950, filed Sep. 5, 1997, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a method for manufacturing a multidomain liquid crystal display panel.
2. Discussion of the Related Art
Generally, a liquid crystal of a liquid crystal display (LCD) panel includes anisotropic molecules. The average direction of the molecules"" long axes is referred to as a director. The director distribution in the liquid crystal is determined by awn anchoring energy of the liquid crystal on a substrate, and is characterized by an orientation of the director corresponding to a minimum of a surface energy of the liquid crystal and the anchoring energy. Reorientation of the director is achieved by applying an external electric field to the liquid crystal.
A basic unit of an LCD panel includes two glass substrates with the liquid crystal positioned between them. To obtain uniform brightness and a high contrast ratio in the LCD panel, it is necessary to homogeneously align the liquid crystal in a liquid crystal cell.
The most common technique for achieving homogeneous alignment includes forming microgrooves on a surface of a polymer. This results in a strong anchoring energy that provides a stable liquid crystal alignment. This technique is called a rubbing method, which is a simple method of rubbing a polymer-coated substrate with a cloth. The rubbing method is widely used, since it is fast and allows for large scale manufacturing.
The rubbing method, however, has several serious drawbacks. Because the shape of the microgrooves formed on the alignment layer depends on the rubbing cloth and a rubbing intensity, the alignment of the liquid crystal is often heterogeneous, causing phase distortion and light scattering. Further, electrostatic discharge (ESD) due to rubbing of a polymer surface generates dust contamination in an active matrix LCD panel, decreasing production yield and damaging the substrate.
In order to solve these problems, a photo-alignment method has been proposed using polarized ultraviolet light irradiated onto a photosensitive polymer (M. Schadt et al., Jpn. J. Appl. Phys., 31 (1992) 2155; T. Ya. Marusii and Yu. A. Reznikov, Mol. Mat., 3 (1993) 161). The alignment capability of a photosensitive polymer is determined by an anisotropy of the photosensitive polymer, which is induced by ultraviolet light irradiation.
Photo-alignment materials used in the LCD panels include polyvinylcinnamate (PVCN) (M. Schadt et al., Jpn. J. Appl. Phys., 31 (1992) 2155), polysiloxane (PS), polyimide (PI), and the like. The photo-alignment properties of these materials appear after the ultraviolet light irradiation by a polarized light.
Moreover, these materials may be used on a base of a silicon polyimide copolymer doped with a diazodiamine dye, or on a base of a polymerizable nematic liquid crystal monomer composition for optical storage (W. M. Gibbons et al., Nature, 351 (1991) 49; P. J. Shannon et al., Nature, 368 (1994) 532). These materials are photosensitive in a visible spectrum.
While the alignment direction of the alignment layer is usually perpendicular to a polarization direction of the ultraviolet light used for irradiation, some materials provide an alignment direction parallel to the polarization direction of the ultraviolet light.
The photo-alignment method has various advantages over the conventional rubbing method. First, there is no electrostatic discharge from a rubbing cloth in rubbing, and therefore, the dust particles do not contaminate the substrate. Second, the photosensitive polymer is able to control the alignment direction and azimuthal anchoring energy of the alignment layer. This, therefore, determines alignment direction in the liquid crystal cell. The photo-alignment method is therefore used to form a multidomain liquid crystal cell, which improves the viewing angle characteristics of the LCD panel.
Several methods are known for forming the multidomain liquid crystal cell using the photo-alignment method.
A method proposed by W. M. Gibbons et al. (Nature, 351 (1991) 49) suggests that after rubbing a photosensitive polymer-coated substrate unidirectionally, the substrate may be irradiated by the ultraviolet light to form an alignment direction perpendicular to the rubbing direction. The LCD panel includes a first substrate, a second substrate rubbed in the same direction as the rubbing direction of the first substrate, and a liquid crystal between the first and second substrates. In the Gibbons method, however, it is necessary to use the rubbing method to make microgrooves in the alignment layer, which still causes problems with the electrostatic discharge and the dust contamination from rubbing.
Modification of the Gibbons method is proposed by P. J. Shannon et al. (Nature, 368 (1994) 532). In the Shannon method, instead of rubbing the alignment layer, the first alignment is performed by irradiating the alignment layer with polarized light. While the Shannon method overcomes the disadvantages of the rubbing method, it has a problem in that in order to change the alignment direction during the manufacturing process, two separate irradiation steps using polarized light are required, with the polarization directions being mutually perpendicular. Several processing steps are therefore needed.
Accordingly, the present invention is directed to a method for manufacturing a multidomain liquid crystal display panel that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for manufacturing a multidomain liquid crystal display panel with a single irradiation step by ultraviolet light and visible light.
Additional features and advantages of the present invention will be set forth in the description which follows, and will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure and process particularly pointed out in the written description as well as in the appended claims.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in accordance with a first aspect of the present invention there is provided a method for manufacturing a multidomain liquid crystal display panel, including the steps of forming a photo-alignment layer on a substrate, positioning a mask having a plurality of regions with different photo. transmittances, and forming different alignment directions in different domains of the photo-alignment layer corresponding to each of the plurality of regions by irradiating the photo-alignment layer with light through the mask.
In another aspect of the present invention there is provided a multidomain liquid crystal display panel, including a first substrate and a second substrate, a liquid crystal positioned between the first substrate and the second substrate, and a photosensitive layer covering the first substrate and having a plurality of first domains and a plurality of second domains, wherein an alignment of photosensitive molecules in the plurality of first domains is orthogonal to alignment of photosensitive molecules in the plurality of second domains, wherein the photosensitive layer includes an ultraviolet light sensitive material and a visible light sensitive material.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.